JP3217490B2 - Semiconductor light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device.

[0002]

2. Description of the Related Art In recent years, semiconductor lasers have been actively developed for application to optical information processing light sources such as optical disk systems and high-speed laser printers. Since shortening the laser oscillation wavelength leads to improvement in the recording density of the optical disc, research and development are being actively conducted. An InGaAlP-based semiconductor laser formed on a GaAs substrate has an oscillation wavelength in the 0.6 μm band, and a 20 mW-class laser at a practical level has already been put into practical use. However, compared to a GaAlAs-based semiconductor laser, hand,
The recording density is only improved to about 1.4 times and is not always sufficient. On the other hand, II-V centered on ZnSe
The group I compound semiconductor can emit blue light at around 0.5 μm, and the recording density is improved three times as compared with a GaAlAs-based semiconductor laser. For this reason, the development of ZnSe-based semiconductor lasers has been particularly vigorous.

In general, p-type ZnSe has a problem that it is difficult to obtain good ohmic contact with a metal electrode. As a means for solving this, G Zn is applied between ZnSe and the metal electrode.
There is a method of providing a contact layer such as aAs. However, in such a semiconductor light emitting device, ZnSe is 2.
7 eV and GaAs have a very large band gap difference of 1.4 eV, and the hetero barrier based on this large band gap difference becomes a barrier against holes, so that ZnSe
It has been clarified that the voltage drop between the heterojunction of GaAs and GaAs becomes significantly large.

[0004]

As described above, the conventional Zn
In a semiconductor light emitting device containing Se, when a GaAs layer is used as a contact layer, there is a problem that a device voltage is significantly increased due to the presence of a hetero barrier based on a large band gap difference.

[0005] The present invention eliminates the above-mentioned problems and removes p from the electrode.
It is an object of the present invention to provide a semiconductor light emitting device in which holes are smoothly injected into the ZnSe layer on the side, and the device voltage is low and the temperature characteristics are remarkably excellent.

[0006]

In order to achieve the above object, a semiconductor light emitting device according to a first aspect of the present invention comprises a first semiconductor layer formed on a substrate and having a surface containing a group II element and a group VI element. A light emitting region, a second semiconductor layer formed on the surface of the first semiconductor layer, having a lattice constant different from the lattice constant of the substrate by 2% or more, and having a film thickness equal to or less than a critical film thickness; And an electrode formed thereon.

A semiconductor light emitting device according to a second aspect of the present invention
A light emitting region formed on a substrate and having a surface formed of a first semiconductor layer containing a group II element and a group VI element; and a lattice constant formed on the surface of the first semiconductor layer and having a lattice constant different from that of the substrate by 2% or more. A second semiconductor layer having a thickness equal to or less than a critical thickness, a III-V semiconductor layer formed on the second semiconductor layer, and an electrode formed on the III-V semiconductor layer. It is characterized by having. Preferably, the group II element is Zn or Cd, and the group VI element is S or Se.
Is fine.

Here, the light emitting region has a light emitting layer that emits light at least by recombination of carriers.
In addition, a cladding layer for confining carriers or light,
It includes a light guide layer that guides emitted light or a growth protection layer that protects the interface of the growth layer.

Further, the critical film thickness is the maximum film thickness at which the lattice can be continuously joined in a strained state without causing a transition when the second semiconductor is grown.

[0010]

According to the present invention, the second semiconductor layer on the surface of the first semiconductor layer containing a group II element and a group VI element has heavy holes when the substrate has a lattice constant ratio of strain of 2% or more. And light holes are separated by strain, the hole coupling with the first semiconductor layer containing the group II element and the group VI element becomes very good, and the hole injection due to the presence of the hetero barrier is prevented. No interference occurs, and holes injected from the electrodes are smoothly injected into the light emitting region. Accordingly, the operating voltage can be sufficiently reduced, and carriers can be effectively injected into the light emitting region.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments. FIG. 1 is a schematic sectional view of a semiconductor laser device according to a first embodiment of the present invention.

On the n-GaAs substrate 11, an n-ZnSe buffer layer 14, which is a light emitting region 25, is provided via an n-GaAs buffer layer 12 and an n-ZnSe buffer layer 13.
ZnSe light guide layer 15, n-ZnCdSe active layer 1
6, a ZnSe light guide layer 17, a p-ZnSSe cladding layer 18, and a p-ZnSe growth protection layer 19 are formed in this order to form a double heterostructure. A p-Zn _0.7 Cd _0.3 Se semiconductor layer 20 as a second semiconductor layer is formed on the surface of a p-ZnSe growth protection layer 19 as a first semiconductor layer containing a group II element and a group VI element forming the surface of the light emitting region 25. Is formed, and a p-GaAs semiconductor layer 21 as a III-V group semiconductor layer is formed on the surface of the p-Zn _0.7 Cd _0.3 Se semiconductor layer 20.

A metal electrode 23 is deposited on the upper surface of the p-GaAs semiconductor layer 21, and a metal electrode 2 is formed on the lower surface of the substrate 11.
4 are applied. All the layers except for the electrode portion are grown by molecular beam epitaxy. In this laser, current confinement is achieved by the dielectric film 22 (SiO ₂ ). Hereinafter, the relationship between the band gap and the device voltage of the second semiconductor layer whose lattice constant differs from the substrate 11 by 2% or more and whose film thickness is equal to or less than the critical film thickness will be described with reference to FIG.

When strain is introduced into the crystal from the state without stress (b), the band structure on the valence band side changes, and heavy holes are generated in both the compression type (a) and the tension type (c). The band _Ehh and the light hole band _Eih are separated by strain. Such a strained layer is formed by p-Z forming the surface of the light emitting region.
When formed in contact with the nSe growth protection layer 19, p-ZnS
The injection of holes from e becomes very good. This is because, in the case of the compression type (a), the positions of the separated light hole band E _ih and the valence band of ZnSe are close to each other, and the level resonance effect and the tunnel effect are increased. This is because, in the case of the tension type (c), the light hole band E _ih jumps out to the forbidden band side, the mobility increases, and the holes easily flow.

In this embodiment, Zn is used as the first semiconductor layer.
_{Although 0.7} Cd _0.3 Se was shown, the lattice constant was larger than the lattice constant of the substrate, resulting in a compression-type band structure, and this composition exceeded 3%. However, the layer thickness is as thin as 50 angstroms (hereinafter referred to as A), and the critical film thickness is 15 Å.
Since it is 0 A or less, it is connected to the adjacent p-ZnSe growth protective layer 19 with a compressive strain, and no dislocation or the like occurs. As a result of the research by the present inventors, it has been found that when the strain amount is 2% or more in terms of the lattice constant ratio, such a strain effect is effective.

Further, as in this embodiment, the second semiconductor layer
The group II-VI group has various merits also in crystal growth, such as good morphology in the preparation of the second semiconductor layer and adjustment of the growth temperature to the light emitting region.

In this embodiment, a GaAs layer is formed as a III-V semiconductor layer between the electrode and the second semiconductor. G
aAs can easily form an alloy layer with Au or the like, and can obtain a low-resistance ohmic contact with the electrode.
It is possible to solve the contact resistance due to heterospikes in the excess electronic band with ZnSe which is a group semiconductor, and to obtain good voltage characteristics. This is to reduce heterospikes in the over-emission band and increase the level of resonance effect and tunnel effect.

Although a high quality GaAs substrate can be obtained, and the growth of each layer described above can be performed with high quality, ZnSe can be used as the substrate in the first embodiment.

FIG. 1 in which the active layer is set to the n-type as described above
When the cavity length was 400 μm, the laser shown in (1) continuously oscillated at room temperature at a threshold value of 80 mA. The resistance of the element is 15Ω, 2
The voltage at 0 mW was also as low as 3.8 V. This is because p-G is directly applied to the surface of the p-ZnSe growth protection layer 18 for comparison.
The voltage at 20 mW when the aAs semiconductor layer is formed is 1
Since the voltage is 0 V, the value is about 1/3, which is a remarkably low value. FIG. 3 is a schematic sectional view of a semiconductor laser device according to a second embodiment of the present invention.

On the n-GaAs substrate 11, an n-ZnSe buffer layer 12, an n-ZnSe buffer layer 13, and an n-ZnSSe cladding layer 14,
ZnSe light guide layer 15, n-ZnCdSe active layer 1
6, a ZnSe light guide layer 17, a p-ZnSSe cladding layer 18, and a p-ZnSe growth protection layer 19 are formed in this order to form a double heterostructure. The above configuration is the first
This is the same as the embodiment. Form the surface of the light emitting region 25
P- which is a first semiconductor layer containing a group II element and a group VI element
On the surface of the ZnSe growth protection layer 19, the second semiconductor layer p
-ZnTe semiconductor layer 40 is formed, and p-InG
A p-GaAs semiconductor layer 21, which is a III-V group semiconductor layer, is formed via an aAlP semiconductor layer 41.

A metal electrode 23 is deposited on the upper surface of the p-GaAs semiconductor layer 21 and a metal electrode 2 is formed on the lower surface of the substrate 11.
4 are applied. All the layers except for the electrode portion are grown by molecular beam epitaxy. In this laser, current confinement is achieved by the dielectric film 22 (SiO ₂ ).

The difference from the first embodiment is the portion above the light emitting region 25, and here ZnTe / InGaAs from below.
The configuration of 1P / GaAs is adopted. ZnTe is advantageous because it can obtain a p-type even if undoped, and the composition control is easy because of the binary composition.

The ZnTe used in this embodiment is a substrate G
Compared with aAs, the lattice constant is different by 3%, and the film thickness is set to 30A which is 100A or less which is the critical film thickness. When the device characteristics of such a laser device were measured in the same manner as in the first embodiment, the voltage at 20 mW was 3.5 V, which was also much lower than that of the comparative example, about 1/3. FIG. 4 is a schematic sectional view of a semiconductor laser device according to a third embodiment of the present invention.

On the n-GaAs substrate 11, an n-ZnSe buffer layer 12, an n-ZnSe buffer layer 13, and an n-ZnSSe clad layer 14,
ZnSe light guide layer 15, n-ZnCdSe active layer 1
6, a ZnSe light guide layer 17, a p-ZnSSe cladding layer 18, and a p-ZnSe growth protection layer 19 are formed in this order to form a double heterostructure. A p-Zn _0.5 Cd _0.5 Se semiconductor layer 60 as a second semiconductor layer is formed on the surface of the p-ZnSe growth protection layer 19 as a first semiconductor layer containing a group II element and a group VI element forming the surface of the light emitting region 25. Is formed on the p-GaAs semiconductor layer 2 which is a III-V group semiconductor layer via a p-In _0.3 Ga _0.7 P semiconductor layer 61.
1 is formed.

A metal electrode 23 is deposited on the upper surface of the p-GaAs semiconductor layer 21, and a metal electrode 2 is formed on the lower surface of the substrate 11.
4 are applied. All the layers except for the electrode portion are grown by molecular beam epitaxy. In this laser, current confinement is achieved by the dielectric film 22 (SiO ₂ ).

The difference from the first and second embodiments lies in the structure above the light emitting region 25. Here, Zn _0.5 Cd
_{The structure is 0.5} Se / In _0.3 Ga _0.7 P / GaAs. This is because the composition of InGaP is In _0.3 Ga _0.7 P
Thus, the lattice constant is set in a direction opposite to the direction of the lattice misalignment of Zn _0.5 Cd _0.5 Se, and the compensation drop of the lattice irregularity is aimed at.

The Zn _0.5 Cd _0.5 Se used in the present embodiment has a lattice constant different from that of GaAs by 2%, and the film thickness is 50 A, which is 100 A or less, which is the critical film thickness. When the element characteristics of such an element were measured in the same manner as in the first embodiment, the voltage at 20 mW was 3.2 V, which was much lower than that of the comparative example, about 1/3.

In these embodiments, only the p-side has a lattice constant different from that of the substrate by 2% or more, and the second film having a film thickness equal to or less than the critical film thickness.
However, in the case of a combination of III-V group semiconductor layer / II-VI group semiconductor layer such as GaAs / ZnSe, the problem of the hetero barrier also becomes a problem on the n-side.
Therefore, it is desirable to provide the same structure as that of the present invention on the n side.

The present invention is not limited to the embodiment described above. The active layer may be a light emitting diode using ZnSe containing no S, or may have a strain introduced. Other As, P, B, as active layers and cladding layers
A material containing N, Zn, Se, or the like may be used.

In the above embodiment, an example of compressive strain was shown. However, if an AlGaP-based strain semiconductor is used, a contact effect as tensile strain can be obtained, and the same effect as in the above embodiment can be expected. . Further, in the above embodiment, an example is shown in which the group III-V contact layer is inserted between the strained semiconductor layer and the electrode, but the strained semiconductor layer and the electrode may be directly connected.

[0031]

As described in detail above, according to the present invention, the operating voltage is remarkably low, so that the temperature characteristics are excellent, the carriers can be effectively injected into the light emitting region, and the light emitting efficiency is remarkably improved. -It is possible to provide a semiconductor light emitting device including a group VI compound semiconductor layer.

[Brief description of the drawings]

FIG. 1 is a sectional view of a semiconductor laser device according to a first embodiment of the present invention.

FIG. 2 is a view for explaining a first embodiment of the present invention and showing a change in band structure in the case where there is no distortion;

FIG. 3 is a sectional view of a semiconductor laser device according to a second embodiment of the present invention.

FIG. 4 is a sectional view of a semiconductor laser device according to a third embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 11 n-GaAs substrate 12 n-GaAs buffer layer 13 n-ZnSe buffer layer 14 n-ZnSSe clad layer 15 ZnSe light guide layer 16 ZnCdSe active layer 17 ZnSe light guide layer 18 p-ZnSSe clad layer 19 p-ZnSe semiconductor layer 20 p-ZnCdSe semiconductor layer 21 p-GaAs semiconductor layer 22 dielectric film 23 metal electrode 24 metal electrode 25 light emitting region

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-97505 (JP, A) JP-A-6-21572 (JP, A) JP-A-6-37356 (JP, A) JP-A-6-37356 85392 (JP, A) JP-A-1-296687 (JP, A) JP-A-60-178684 (JP, A) JP-A-59-184583 (JP, A) JP-A-6-5920 (JP, A) JP-A-5-218565 (JP, A) JP-A-6-13655 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/00-5/50 H01L 33/00

Claims (1)

(57) [Claims] 1. The method according to claim 1, wherein the surface is formed on a substrate and has a surface of a group II element and a VI.
A light emitting region comprising a first semiconductor layer containing a group III element, and a second light emitting region formed on the surface of the first semiconductor layer, having a lattice constant different from the lattice constant of the substrate by 2% or more and having a film thickness equal to or less than a critical film thickness. And a II formed on the second semiconductor layer.
A semiconductor light emitting device comprising: a group IV semiconductor layer; and an electrode formed on the group III-V semiconductor layer.